title: Chemokine unresponsiveness of chronic lymphocytic leukemia cells results from impaired endosomal recycling of Rap1 and is associated with a distinctive type of immunological anergy.
abstract: Trafficking of malignant lymphocytes is fundamental to the biology of chronic lymphocytic leukemia (CLL). Transendothelial migration (TEM) of normal lymphocytes into lymph nodes requires the chemokine-induced activation of Rap1 and αLβ2 integrin. However, in most cases of CLL, Rap1 is refractory to chemokine stimulation, resulting in failed αLβ2 activation and TEM unless α4β1 is coexpressed. In this study, we show that the inability of CXCL12 to induce Rap1 GTP loading in CLL cells results from failure of Rap1-containing endosomes to translocate to the plasma membrane. Furthermore, failure of chemokine-induced Rap1 translocation/GTP loading was associated with a specific pattern of cellular IgD distribution resembling that observed in normal B cells anergized by DNA-based Ags. Anergic features and chemokine unresponsiveness could be simultaneously reversed by culturing CLL cells ex vivo, suggesting that these two features are coupled and driven by stimuli present in the in vivo microenvironment. Finally, we show that failure of Rap1 translocation/GTP loading is linked to defective activation of phospholipase D1 and its upstream activator Arf1. Taken together, our findings indicate that chemokine unresponsiveness in CLL lymphocytes results from failure of Arf1/phospholipase D1-mediated translocation of Rap1 to the plasma membrane for GTP loading and may be a specific feature of anergy induced by DNA Ags.
authors.affiliation: Department of Molecular and Clinical Cancer Medicine, University of Liverpool, Liverpool L69 3GA, United Kingdom.
authors.forename: Derek S
authors.initials: DS
authors.lastname: Pye
authors.forename: Ignacio
authors.initials: I
authors.lastname: Rubio
authors.forename: Rico
authors.initials: R
authors.lastname: Pusch
authors.forename: Ke
authors.initials: K
authors.lastname: Lin
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Pettitt
authors.forename: Kathleen J
authors.initials: KJ
authors.lastname: Till
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology; D002462:Cell Membrane / Q000378:metabolism; D054377:Chemokine CXCL12 / Q000378:metabolism; D017635:Clonal Anergy / Q000276:immunology*; D011992:Endosomes / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D007072:Immunoglobulin D / Q000276:immunology / Q000378:metabolism; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000276:immunology* / Q000378:metabolism; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D008214:Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D057705:Transendothelial and Transepithelial Migration / Q000276:immunology; D014407:Tumor Cells, Cultured; D020668:rap GTP-Binding Proteins / Q000096:biosynthesis
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D007072:Immunoglobulin D; D016169:Lymphocyte Function-Associated Antigen-1; D000089804:Shelterin Complex; C440809:TERF2IP protein, human; D034501:Telomere-Binding Proteins; D010739:Phospholipase D; C106801:phospholipase D1; C116756:RAP2A protein, human; D020823:ADP-Ribosylation Factor 1; D020668:rap GTP-Binding Proteins